Malignant peritoneal effusion, alternatively peritonitis, hemoabdomen or carcinomatosis. Other types of peritoneal effusion could also be considered, but based on the other findings would be less likely.

Recommendations:

Abdominocentesis for cytologic evaluation of the fluid +/- culture.

Ultrasound to further evaluate the liver and spleen, guide fine needle aspiration of the organs and look for other organ involvement not seen on radiographs (ie. lymphadenomegaly or intestinal infiltration.)

Follow up: Mast cell disease was confirmed in the cytology of the liver/spleen and effusion.

Candidate Performance: Many candidates did well on the question correlating all the major radiographic findings into a well thought out, inclusive differential list (one of the skills this case was intended to evaluate). Some candidates described the findings but then only concluded on one of them (ie. loss of detail) or could not put all the findings together into a cohesive differential list. A few candidates either missed major findings (i.e. organomegaly) or described abnormalities that were not present.